Halogen-free rubber conveying belt and preparation process thereof

Abstract

The invention provides a halogen-free rubber conveyor belt and a preparation process thereof, and belongs to the technical field of rubber conveyor belts, and the preparation process comprises the following steps: mixing, stirring, cooling and drying n-hexylphosphoric acid, ethanol and a magnesium hydroxide suspension to prepare modified magnesium hydroxide; the method comprises the following steps: grinding steel slag powder, adding absolute ethyl alcohol and a sorbic acid solution, stirring for reaction, centrifuging, taking precipitate, and drying to obtain modified steel slag; the rubber, the modified steel slag, the carbon black, the modified magnesium hydroxide and the auxiliaries are added into a double-roller open mill to be evenly mixed, thin-passing and calendaring are conducted to form sheets, then the sheets, aramid fiber cloth subjected to surface treatment and a steel wire rope are subjected to compression molding, and vulcanization is conducted to prepare the halogen-free rubber conveying belt. The flame retardant property of the rubber conveying belt is improved, and meanwhile the mechanical strength and the high-temperature resistance are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of rubber conveyor belts, and particularly to a halogen-free rubber conveyor belt and a preparation process thereof. Background Art

[0002] Steel cord conveyor belts are often used in heavy-duty and long-distance material transportation. Current steel cord conveyor belts are mainly divided into two categories: ordinary-purpose steel cord conveyor belts and coal mine special steel cord flame-retardant conveyor belts. For industries such as metallurgy, building materials, and chemical engineering, it is often necessary to transport some high-temperature materials, such as sintered ore, pellet ore, cement clinker, lime, coke, and chemical fertilizers. These materials are prone to causing fires during transportation. Therefore, the requirements for steel cord conveyor belts in these industries are more stringent. They need to have both flame-retardant properties and good high-temperature resistance to ensure that they will not be ignited or damaged under high-temperature conditions.

[0003] Most traditional flame-retardant conveyor belts use halogen elements as flame-retardant components, which have a strong flame-retardant effect and improve the flame-retardant properties of materials. However, when the conveyor belt catches fire in a high-temperature or fire environment, the halogen will react with the chemical substances generated by thermal decomposition, releasing a large amount of toxic gases and accompanied by thick smoke. This not only pollutes the air but may also have a serious impact on the health of workers, equipment, and the environment. To avoid using halogen flame retardants and reduce the impact on the environment and human health, researchers have developed a variety of halogen-free flame retardants suitable for conveyor belts. These halogen-free flame retardants are generally composed of environmentally friendly materials such as metal hydroxides, phosphates, and inorganic compounds. They can absorb heat and form a carbonized layer during combustion, hindering the spread of flames, thereby effectively reducing the risk of fire and avoiding the release of toxic gases.

[0004] The patent application document with the publication number CN117183500B discloses a non-antimony high-wear-resistant flame-retardant conveyor belt and a preparation method thereof, including a rubber covering layer and a carcass layer; the raw materials of the rubber covering layer include nitrile rubber, a composite flame retardant, fillers, sulfur, stearic acid, zinc oxide, and an antioxidant; the composite flame retardant is composed of magnesium hydroxide, borate, and phosphate ester; the raw materials of the carcass layer are aramid fiber cloth. Through the above technical solution, the problems in the prior art of poor flame retardancy of nitrile rubber conveyor belts, poor adhesion between the rubber covering layer and the carcass layer, and environmental unfriendliness of using antimony-containing flame retardants are solved. However, the dispersion of magnesium hydroxide flame retardant in the body is poor, which affects the mechanical properties.

[0005] Therefore, it is necessary to provide a halogen-free rubber conveyor belt and a preparation process thereof to solve the problems existing in the above prior art. Summary of the Invention

[0006] In view of this, the present invention provides a halogen-free rubber conveyor belt and a preparation process thereof, which can improve the flame retardant performance of the rubber conveyor belt while improving the mechanical strength and high temperature resistance.

[0007] To achieve the above object, the present invention provides a preparation process of a halogen-free rubber conveyor belt, comprising the following steps: S1. Mix and stir n-hexylphosphoric acid and ethanol, and dropwise add them into a magnesium hydroxide suspension, stir, cool, wash, and vacuum dry to obtain modified magnesium hydroxide; S2. Grind steel slag powder, add anhydrous ethanol and mix and stir, add sorbic acid solution, stir and react, centrifuge to obtain precipitate, wash, and dry to obtain modified steel slag; S3. Immerse the pretreated aramid fiber cloth in KH-560 solution to obtain a surface-treated aramid fiber cloth; S4. Add rubber, modified steel slag, carbon black, modified magnesium hydroxide, stearic acid, zinc oxide, crosslinking agent and sulfur into a two-roll open mill for mixing, thin pass, calender into sheets, and then press and form with the surface-treated aramid fiber cloth, and vulcanize to obtain a halogen-free rubber conveyor belt.

[0008] In the present invention, n-hexylphosphoric acid is used to modify the surface of magnesium hydroxide by esterification. Magnesium hydroxide absorbs heat through an endothermic decomposition reaction, absorbs heat from the surrounding, and releases water vapor / carbon dioxide, thereby protecting the matrix from the influence of oxygen. However, due to its hydrophilic surface, the dispersion of magnesium hydroxide particles in hydrophobic rubber is poor, and they are prone to aggregation, and the combination with the rubber matrix is not good, which affects the mechanical properties of the rubber matrix and weakens the flame retardant effect. By introducing n-hexylphosphoric acid, the hydrophobic group of n-hexylphosphoric acid can improve the compatibility between magnesium hydroxide and rubber, thereby enhancing the dispersion; and the phosphate group in n-hexylphosphoric acid has a free radical stabilizing effect by capturing free radicals during the combustion process of hydrocarbons, so that it can slow down the OH - release rate, so that n-hexylphosphoric acid and magnesium hydroxide produce a synergistic effect on thermal stability, delay the decomposition temperature of magnesium hydroxide, and enable it to play a role at a higher temperature, improving the high temperature resistance. The phosphate group forms a P-Mg-O bond with magnesium hydroxide, synergistically promoting the formation of a dense carbon layer and also enhancing the flame retardant effect.

[0009] In the present invention, sorbic acid is used to make the surface of steel slag organic, and the obtained modified steel slag replaces most of the carbon black. Steel slag itself contains metal oxides and can be used as a reinforcing filler, but its surface is hydrophilic and it is difficult to combine with rubber. Sorbic acid contains a carboxylic acid group and can form a chemical bond with the metal oxides on the surface of steel slag to enhance the interfacial combination. The modified steel slag has better dispersion in rubber and better reinforcing effect. At the same time, the CaO / SiO2 component in steel slag forms a calcium silicate network at high temperature, which can improve the overall high temperature resistance.

[0010] The present invention utilizes aramid fibers and steel wires together as the reinforcing layer of the halogen-free rubber conveyor belt. The steel wires provide high-rigidity longitudinal tensile strength, while the aramid fibers, due to their high modulus and low density, can form a tear-resistant network structure in the transverse direction to prevent local fracture caused by stress concentration. Additionally, the steel wires and aramid fibers have good high-temperature resistance and can maintain good physical properties in a high-temperature environment. Moreover, the addition of aramid fibers can effectively block the spread of flames. Here, after the aramid fiber cloth is treated with KH-560 silane coupling agent, a stable silane layer is formed on the fiber surface. This layer not only improves the adhesion strength between the aramid fibers and the rubber matrix but also enhances their interfacial compatibility, significantly improving the overall mechanical properties of the composite material.

[0011] Optionally, the magnesium hydroxide suspension is prepared by mixing magnesium hydroxide particles and absolute ethanol and subjecting them to ultrasonic treatment for 5 - 10 min.

[0012] Optionally, in step S1, n-hexylphosphoric acid and ethanol are mixed and stirred for 10 - 15 min, then added dropwise to the magnesium hydroxide suspension. After evacuating the air, it is stirred at a speed of 2000 r / min for 10 - 20 min, then heated to 170 °C and stirred at a speed of 300 r / min for 6 h. After cooling to room temperature, it is washed 2 - 3 times with absolute ethanol and vacuum dried at room temperature for 8 - 12 h to obtain modified magnesium hydroxide.

[0013] In the process of preparing modified magnesium hydroxide in the present invention, washing with absolute ethanol helps to remove unreacted solvents, surface residues, and by-products, ensuring the purity and performance of the modified magnesium hydroxide.

[0014] Optionally, in step S2, the mixing and stirring speed is 500 r / min and the time is 10 min, the stirring reaction temperature is 80 - 150 °C and the time is 2 - 3 h, it is washed 2 - 3 times with absolute ethanol, and the drying temperature is 100 - 120 °C and the time is 6 h.

[0015] Preferably, in step S2, the steel slag is ground to a particle size less than 100 mesh.

[0016] In the present invention, grinding the steel slag powder to a particle size less than 100 mesh can significantly increase its surface activity and the reaction rate with other chemical substances, improving the modification effect.

[0017] Optionally, the mass concentration of the sorbic acid solution in step S2 is 14%.

[0018] Optionally, the pretreated aramid fiber cloth is prepared by ultrasonically cleaning the aramid fiber cloth with acetone for 1 h, washing it with deionized water 3 - 5 times, impregnating it in a 5% CaCl₂ ethanol solution for 5 h, then immersing it in a 10% NaOH aqueous solution and impregnating at 65 °C for 3 - 5 h, rinsing with deionized water 2 - 3 times, and air-drying.

[0019] The present invention uses a CaCl₂ ethanol solution to increase the surface roughness and treats it with an NaOH solution to hydrolyze aromatic fibers and break the amide bonds on the molecular chain, thereby forming carboxylic acid groups and primary amines, thus improving the surface activity of aramid fibers and enhancing their binding ability with other materials.

[0020] Optionally, in step S3, the pretreated aramid fiber cloth is immersed in a 10% KH-560 solution and impregnated at 40 °C for 3 - 5 h to obtain the surface-treated aramid fiber cloth.

[0021] Optionally, in step S4, the rubber is natural rubber, silicone rubber, and carboxy styrene butadiene rubber, the crosslinking agent is di-tert-butyl peroxide, and antioxidant 1010 is also added when adding the crosslinking agent.

[0022] Optionally, the mixing in step S4 is carried out at 45 - 70 °C, the number of thin passes is 5 - 7 times, the vulcanization temperature is 160 °C, and the time is 30 - 50 min.

[0023] Optionally, the halogen-free rubber conveyor belt comprises the following raw materials in parts by mass: 100 parts of rubber, 20 - 30 parts of modified steel slag, 10 - 20 parts of carbon black, 10 - 15 parts of modified magnesium hydroxide, 8 - 10 parts of stearic acid, 2 - 3 parts of zinc oxide, 0.3 - 0.5 parts of crosslinking agent, 5 - 7 parts of sulfur, and 1 - 2 parts of antioxidant 1010.

[0024] The present invention adopts the above mass ratio matching, which can improve the overall performance of the halogen-free rubber conveyor belt in many aspects.

[0025] The above technical solutions of the present invention have at least the following beneficial effects: 1. The present invention modifies the surface of magnesium hydroxide by n-hexyl phosphoric acid esterification, improves its compatibility with the rubber matrix, and enhances the dispersibility. The hydrophobic group of n-hexyl phosphoric acid enhances the binding of magnesium hydroxide to the rubber and reduces the aggregation phenomenon. Magnesium hydroxide protects the matrix through an endothermic decomposition reaction, and the phosphate group in n-hexyl phosphoric acid stabilizes free radicals and delays the OH - release rate, synergistically improving the thermal stability. In addition, the phosphate group forms a P-Mg-O bond with magnesium hydroxide, promoting the formation of a dense carbon layer and further enhancing the flame retardant effect.

[0026] 2. The present invention modifies steel slag by treatment with sorbic acid to make its surface organic, enhancing the interfacial bonding between the steel slag and the rubber. The carboxylic acid groups of sorbic acid form chemical bonds with the metal oxides on the surface of the steel slag, improving the dispersibility and reinforcing effect of the steel slag. Meanwhile, the CaO / SiO2 components in the steel slag form a calcium silicate network at high temperature, enhancing the high-temperature resistance of the rubber.

[0027] 3. The present invention uses aramid fibers and steel wire ropes as the reinforcing layers of the halogen-free rubber conveyor belt. The steel wire ropes provide longitudinal tensile strength, and the aramid fibers form a tear-resistant network to enhance the transverse strength. Both of them have excellent high-temperature resistance and can block the spread of flames. After treatment with KH-560 silane coupling agent, a stable silane layer is formed on the surface of the aramid fibers, enhancing the adhesion strength and interfacial compatibility between the fibers and the rubber matrix, thus significantly improving the mechanical properties of the composite material. Detailed implementation manners

[0028] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. The described embodiments are part of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the described embodiments of the present invention fall within the scope of protection of the present invention.

[0029] Example 1 Mix 50 parts of magnesium hydroxide particles and 500 parts of absolute ethanol, and ultrasonically treat for 10 min to obtain a magnesium hydroxide suspension; mix 16 parts of n-hexyl phosphoric acid and 100 parts of ethanol, stir for 15 min, and gradually add it dropwise to the magnesium hydroxide suspension. After evacuating the air, stir at a speed of 2000 r / min for 20 min, then raise the temperature to 170 °C, stir at a speed of 300 r / min for 6 h, cool to room temperature, wash 3 times with absolute ethanol, and vacuum dry at room temperature for 12 h to obtain modified magnesium hydroxide.

[0030] Pour 100 parts of steel slag powder, which has been ground to a particle size less than 100 mesh, into a 250-part three-necked flask, add 100 parts of absolute ethanol, stir at a speed of 500 r / min for 10 min, slowly add 300 parts of a 14% sorbic acid solution by mass concentration, stir and react at 150 °C for 3 h, centrifuge to obtain the precipitate, wash 3 times with absolute ethanol, and dry at 120 °C for 6 h to obtain modified steel slag.

[0031] The aramid fiber cloth was ultrasonically cleaned with acetone for 1 h, washed 5 times with deionized water, impregnated in a 5% CaCl2 ethanol solution for 5 h, then immersed in a 10% NaOH aqueous solution, impregnated at 65 °C for 5 h, rinsed 3 times with deionized water, and air-dried to obtain the pretreated aramid fiber cloth; the pretreated aramid fiber cloth was immersed in a 10% KH-560 solution and impregnated at 40 °C for 5 h to obtain the surface-treated aramid fiber cloth.

[0032] On a two-roll mill, 10 parts of natural rubber, 30 parts of silicone rubber, and 60 parts of carboxylated styrene-butadiene rubber were added, the roll temperature of the mill was controlled at 50 °C, 30 parts of modified steel slag, 10 parts of carbon black, 15 parts of modified magnesium hydroxide, 10 parts of stearic acid, 3 parts of zinc oxide, 2 parts of antioxidant 1010 were added in sequence, and finally 0.5 part of crosslinking agent di-tert-butyl peroxide and 7 parts of sulfur were added. The roll temperature of the mill was controlled at 70 °C, and they were mixed evenly on the mill. Then the roll gap of the mill was adjusted to 1 mm, the roll temperature was 50 °C, and it was passed through thinly 7 times to obtain the mixed rubber.

[0033] The mixed rubber was remilled in a mill and then calendered into sheets in a calender to obtain the cover layer. Then, on a molding machine, according to the structure of cover layer - surface-treated aramid fiber cloth - steel wire rope - surface-treated aramid fiber cloth - cover layer, the cover layer, surface-treated aramid fiber cloth, and steel wire rope were pressed and molded, and placed in a flat vulcanizer to be vulcanized at 160 °C for 50 min to obtain the halogen-free rubber conveyor belt.

[0034] Example 2 30 parts of magnesium hydroxide particles and 500 parts of absolute ethanol were mixed and ultrasonically treated for 5 min to obtain a magnesium hydroxide suspension; 16 parts of n-hexyl phosphoric acid and 100 parts of ethanol were mixed and stirred for 10 min, and then added dropwise to the magnesium hydroxide suspension. After evacuating, it was stirred at a speed of 2000 r / min for 10 min, then heated to 170 °C and stirred at a speed of 300 r / min for 6 h. After cooling to room temperature, it was washed 2 times with absolute ethanol and vacuum-dried at room temperature for 8 h to obtain the modified magnesium hydroxide.

[0035] 100 parts of steel slag powder, after being ground to a particle size less than 100 mesh, was poured into a 250-part three-necked flask, 100 parts of absolute ethanol was added, and it was stirred at a speed of 500 r / min for 10 min. 300 parts of a 14% sorbic acid solution was slowly added, and it was stirred and reacted at 80 °C for 3 h. After centrifuging to take the precipitate, it was washed 2 times with absolute ethanol and dried at 100 °C for 6 h to obtain the modified steel slag.

[0036] The aramid fiber cloth was ultrasonically cleaned with acetone for 1 h, washed 3 times with deionized water, immersed in a 5% mass concentration of CaCl₂ ethanol solution for 5 h, then immersed in a 10% mass concentration of NaOH aqueous solution, and immersed at 65 °C for 3 h. After being rinsed 2 times with deionized water and air-dried, the pretreated aramid fiber cloth was obtained; the pretreated aramid fiber cloth was immersed in a 10% mass concentration of KH-560 solution and immersed at 40 °C for 3 h to obtain the surface-treated aramid fiber cloth.

[0037] On a two-roll mill, 20 parts of natural rubber, 30 parts of silicone rubber, and 50 parts of carboxylated styrene-butadiene rubber were added. The roll temperature of the mill was controlled at 30 °C. 20 parts of modified steel slag, 20 parts of carbon black, 10 parts of modified magnesium hydroxide, 8 parts of stearic acid, 2 parts of zinc oxide, 1 part of antioxidant 1010 were added in sequence. Finally, 0.3 part of crosslinking agent di-tert-butyl peroxide and 5 parts of sulfur were added. The roll temperature of the mill was controlled at 45 °C, and the mixture was uniformly mixed on the mill. Then the roll gap of the mill was adjusted to 0.5 mm, the roll temperature was 40 °C, and it was passed through thinly 5 times to obtain the mixed rubber.

[0038] The mixed rubber was remilled in the mill, then placed in a calender to calender and produce a cover layer. After that, on a molding machine, according to the structure of cover layer - surface-treated aramid fiber cloth - steel wire rope - surface-treated aramid fiber cloth - cover layer, the cover layer, surface-treated aramid fiber cloth, and steel wire rope were pressed and molded, and then placed in a flat vulcanizer and vulcanized at 160 °C for 30 min to obtain the halogen-free rubber conveyor belt.

[0039] Example 3 35 parts of magnesium hydroxide particles and 500 parts of absolute ethanol were mixed and ultrasonically treated for 6 min to obtain a magnesium hydroxide suspension; 16 parts of n-hexyl phosphoric acid and 100 parts of ethanol were mixed and stirred for 12 min, and then added dropwise to the magnesium hydroxide suspension. After evacuating, it was stirred at a speed of 2000 r / min for 18 min, then heated to 170 °C and stirred at a speed of 300 r / min for 6 h. After cooling to room temperature, it was washed 3 times with absolute ethanol and vacuum dried at room temperature for 10 h to obtain modified magnesium hydroxide.

[0040] 100 parts of steel slag powder, after being ground to a particle size less than 100 mesh, were poured into a 250 mL three-necked flask, 100 parts of absolute ethanol were added, and it was stirred at a speed of 500 r / min for 10 min. 300 parts of a 14% mass concentration of sorbic acid solution were slowly added, and it was stirred and reacted at 120 °C for 2.5 h. After centrifuging to collect the precipitate, it was washed 3 times with absolute ethanol and dried at 100 °C for 6 h to obtain modified steel slag.

[0041] The aramid fiber cloth was ultrasonically cleaned with acetone for 1 h, washed 4 times with deionized water, impregnated in a 5% mass concentration of CaCl₂ ethanol solution for 5 h, then immersed in a 10% mass concentration of NaOH aqueous solution, impregnated at 65 °C for 4 h, rinsed 3 times with deionized water, and air-dried to obtain the pretreated aramid fiber cloth; the pretreated aramid fiber cloth was immersed in a 10% mass concentration of KH-560 solution and impregnated at 40 °C for 4 h to obtain the surface-treated aramid fiber cloth.

[0042] On a two-roll mill, 15 parts of natural rubber, 30 parts of silicone rubber, and 55 parts of carboxylated styrene-butadiene rubber were added, the roll temperature of the mill was controlled at 40 °C, 28 parts of modified steel slag, 12 parts of carbon black, 14 parts of modified magnesium hydroxide, 9 parts of stearic acid, 2.7 parts of zinc oxide, 1.8 parts of antioxidant 1010 were added in sequence, and finally 0.4 parts of crosslinking agent di-tert-butyl peroxide and 6 parts of sulfur were added. The roll temperature of the mill was controlled at 70 °C, mixed evenly on the mill, then the roll gap of the mill was adjusted to 1 mm, the roll temperature was 50 °C, and thin-sliced 6 times to obtain the mixed rubber.

[0043] The mixed rubber was remilled in a mill, then calendered into sheets in a calender to obtain the cover layer. After that, on a molding machine, according to the structure of cover layer - surface-treated aramid fiber cloth - steel wire rope - surface-treated aramid fiber cloth - cover layer, the cover layer, surface-treated aramid fiber cloth, and steel wire rope were pressed and formed, and placed in a flat vulcanizer to vulcanize at 160 °C for 45 min to obtain the halogen-free rubber conveyor belt.

[0044] Example 4 35 parts of magnesium hydroxide particles and 500 parts of absolute ethanol were mixed and ultrasonically treated for 8 min to obtain a magnesium hydroxide suspension; 16 parts of n-hexyl phosphoric acid and 100 parts of ethanol were mixed and stirred for 11 min, and gradually added dropwise to the magnesium hydroxide suspension. After evacuating, stirred at a speed of 2000 r / min for 15 min, then heated to 170 °C, stirred at a speed of 300 r / min for 6 h, cooled to room temperature, washed 3 times with absolute ethanol, and vacuum dried at room temperature for 8 h to obtain modified magnesium hydroxide.

[0045] 100 parts of steel slag powder, after being ground to a particle size less than 100 mesh, was poured into a 250-part three-necked flask, 100 parts of absolute ethanol was added, stirred at a speed of 500 r / min for 10 min, 300 parts of a 14% mass concentration of sorbic acid solution was slowly added, stirred and reacted at 110 °C for 2 h. After centrifuging to collect the precipitate, it was washed 3 times with absolute ethanol and dried at 110 °C for 6 h to obtain modified steel slag.

[0046] The aramid fiber cloth was ultrasonically cleaned with acetone for 1 h, washed 3 times with deionized water, immersed in a 5% mass concentration of CaCl2 ethanol solution for 5 h, then immersed in a 10% mass concentration of NaOH aqueous solution, and immersed at 65 °C for 3 h, rinsed 2 times with deionized water, and air-dried to obtain the pretreated aramid fiber cloth; the pretreated aramid fiber cloth was immersed in a 10% mass concentration of KH-560 solution and immersed at 40 °C for 3.5 h to obtain the surface-treated aramid fiber cloth.

[0047] On a two-roll mill, 15 parts of natural rubber, 30 parts of silicone rubber, and 55 parts of carboxylated styrene-butadiene rubber were added, the roll temperature of the mill was controlled at 40 °C, 22 parts of modified steel slag, 18 parts of carbon black, 11 parts of modified magnesium hydroxide, 8 parts of stearic acid, 3 parts of zinc oxide, 1.2 parts of antioxidant 1010 were added in sequence, and finally 0.3 parts of crosslinking agent di-tert-butyl peroxide and 5.5 parts of sulfur were added. The roll temperature of the mill was controlled at 60 °C, mixed evenly on the mill, then the roll gap of the mill was adjusted to 0.5 mm, the roll temperature was 40 °C, and thin-sliced 6 times to obtain the mixed rubber.

[0048] The mixed rubber was remilled in a mill, then calendered into sheets in a calender to obtain the cover layer. After that, on a molding machine, according to the structure of cover layer-surface-treated aramid fiber cloth-steel wire rope-surface-treated aramid fiber cloth-cover layer, the cover layer, the surface-treated aramid fiber cloth and the steel wire rope were pressed and formed, and placed in a flat vulcanizer to vulcanize at 160 °C for 35 min to obtain the halogen-free rubber conveyor belt.

[0049] Example 5 40 parts of magnesium hydroxide particles and 500 parts of absolute ethanol were mixed and ultrasonically treated for 6 min to obtain a magnesium hydroxide suspension; 16 parts of n-hexyl phosphoric acid and 100 parts of ethanol were mixed and stirred for 12 min, and gradually added dropwise to the magnesium hydroxide suspension, evacuated, stirred at a speed of 2000 r / min for 15 min, then heated to 170 °C, stirred at a speed of 300 r / min for 6 h, cooled to room temperature, rinsed 2 times with absolute ethanol, and vacuum dried at room temperature for 9 h to obtain modified magnesium hydroxide.

[0050] 100 parts of steel slag powder, ground to a particle size less than 100 mesh, was poured into a 250-part three-necked flask, 100 parts of absolute ethanol was added, stirred at a speed of 500 r / min for 10 min, 300 parts of a 14% mass concentration of sorbic acid solution was slowly added, stirred and reacted at 90 °C for 3 h, the precipitate was centrifuged and taken, washed 3 times with absolute ethanol, and dried at 110 °C for 6 h to obtain modified steel slag.

[0051] The aramid fiber cloth was ultrasonically cleaned with acetone for 1 h, washed 4 times with deionized water, impregnated in a 5% CaCl₂ ethanol solution for 5 h, then immersed in a 10% NaOH aqueous solution, impregnated at 65 °C for 4.5 h, rinsed 3 times with deionized water, and air-dried to obtain the pretreated aramid fiber cloth; the pretreated aramid fiber cloth was immersed in a 10% KH-560 solution and impregnated at 40 °C for 4 h to obtain the surface-treated aramid fiber cloth.

[0052] On a two-roll mill, 11 parts of natural rubber, 30 parts of silicone rubber, and 59 parts of carboxylated styrene-butadiene rubber were added, the roll temperature of the mill was controlled at 50 °C, 20 parts of modified steel slag, 20 parts of carbon black, 15 parts of modified magnesium hydroxide, 9 parts of stearic acid, 2.6 parts of zinc oxide, 1.4 parts of antioxidant 1010 were added in sequence, and finally 0.5 part of crosslinking agent di-tert-butyl peroxide and 6 parts of sulfur were added. The roll temperature of the mill was controlled at 60 °C, and the mixture was uniformly mixed on the mill. Then the roll gap of the mill was adjusted to 0.5 mm, the roll temperature was 50 °C, and it was passed through thinly 7 times to obtain the mixed rubber.

[0053] The mixed rubber was remilled in the mill, then calendered into sheets in a calender to obtain the cover layer. After that, on a molding machine, according to the structure of cover layer - surface-treated aramid fiber cloth - steel wire rope - surface-treated aramid fiber cloth - cover layer, the cover layer, surface-treated aramid fiber cloth, and steel wire rope were pressed and molded, and then placed in a flat vulcanizer and vulcanized at 160 °C for 40 min to obtain the halogen-free rubber conveyor belt.

[0054] Example 6 40 parts of magnesium hydroxide particles and 500 parts of absolute ethanol were mixed and ultrasonically treated for 5 min to obtain a magnesium hydroxide suspension; 16 parts of n-hexyl phosphoric acid and 100 parts of ethanol were mixed and stirred for 15 min, and then added dropwise to the magnesium hydroxide suspension. After evacuating, it was stirred at a speed of 2000 r / min for 17 min, then heated to 170 °C and stirred at a speed of 300 r / min for 6 h. After cooling to room temperature, it was washed 3 times with absolute ethanol and vacuum dried at room temperature for 11 h to obtain the modified magnesium hydroxide.

[0055] 100 parts of steel slag powder, after being ground to a particle size less than 100 mesh, were poured into a 250-part three-necked flask, 100 parts of absolute ethanol were added, and it was stirred at a speed of 500 r / min for 10 min. Then 300 parts of a 14% sorbic acid solution were slowly added, and it was stirred and reacted at 150 °C for 3 h. After centrifuging to collect the precipitate, it was washed 2 times with absolute ethanol and dried at 120 °C for 6 h to obtain the modified steel slag.

[0056] The aramid fiber cloth was ultrasonically cleaned with acetone for 1 h, washed 3 times with deionized water, impregnated in a 5% CaCl2 ethanol solution for 5 h, then immersed in a 10% NaOH aqueous solution, impregnated at 65 °C for 5 h, rinsed 2 times with deionized water, and air-dried to obtain the pretreated aramid fiber cloth; the pretreated aramid fiber cloth was immersed in a 10% KH-560 solution and impregnated at 40 °C for 3 h to obtain the surface-treated aramid fiber cloth.

[0057] On a two-roll mill, 14 parts of natural rubber, 30 parts of silicone rubber, and 56 parts of carboxylated styrene-butadiene rubber were added. The roll temperature of the mill was controlled at 40 °C. 28 parts of modified steel slag, 12 parts of carbon black, 13 parts of modified magnesium hydroxide, 10 parts of stearic acid, 2 parts of zinc oxide, 1 part of antioxidant 1010 were added in sequence. Finally, 0.3 parts of crosslinking agent di-tert-butyl peroxide and 5 parts of sulfur were added. The roll temperature of the mill was controlled at 70 °C, and the mixture was uniformly mixed on the mill. Then the roll gap of the mill was adjusted to 1 mm, the roll temperature was 40 °C, and it was passed through thinly 6 times to obtain the mixed rubber.

[0058] The mixed rubber was remilled in a mill and then calendered into sheets in a calender to obtain the cover layer. Then, on a molding machine, according to the structure of cover layer - surface-treated aramid fiber cloth - steel wire rope - surface-treated aramid fiber cloth - cover layer, the cover layer, the surface-treated aramid fiber cloth, and the steel wire rope were pressed and molded, and then placed in a flat vulcanizer and vulcanized at 160 °C for 40 min to obtain the halogen-free rubber conveyor belt.

[0059] The present invention also carried out comparative examples and related tests.

[0060] Comparative Example 1 Compared with Example 1, the difference was only that magnesium hydroxide was not prepared and magnesium hydroxide was directly added, and other preparation steps and components remained unchanged. Finally, a halogen-free rubber conveyor belt was obtained.

[0061] Comparative Example 2 Compared with Example 1, the difference was only that modified steel slag was not prepared and steel slag was directly added, and other preparation steps and components remained unchanged. Finally, a halogen-free rubber conveyor belt was obtained.

[0062] Comparative Example 3 Compared with Example 1, the difference was only that the surface-treated aramid fiber cloth was not prepared and aramid fiber cloth was directly added, and other preparation steps and components remained unchanged. Finally, a halogen-free rubber conveyor belt was obtained.

[0063] Performance detection test The halogen-free rubber conveyor belts prepared in Examples 1 to 6 and Comparative Examples 1 to 3 were tested for relevant properties according to the national standard of MT / T 668-2019 Steel Wire Rope Core Flame Retardant Conveyor Belts for Coal Mines and the test methods of GB / T 528-2009 Determination of Tensile Stress-Strain Properties of Vulcanized Rubber or Thermoplastic Rubber and GB / T 3512-2014 Heat Air Accelerated Aging and Heat Resistance Test of Vulcanized Rubber or Thermoplastic Rubber. The specific test results are shown in Table 1 and Table 2.

[0064] Table 1

[0065] As can be seen from Table 1, the relevant mechanical properties of the halogen-free rubber conveyor belt prepared by the present invention have all met the national standard requirements of MT / T 668-2019 Steel Wire Rope Core Flame Retardant Conveyor Belts for Coal Mines.

[0066] Combined with the data in Table 1, in Example 1, the surface treatment of aramid fibers significantly improved the adhesion strength between the steel wire rope and the adhesion strength between the cover layer and the aramid fiber layer. Moreover, the overall bonding strength increased after the modification of magnesium hydroxide and steel slag, which also significantly improved the overall tensile strength, tear strength and elongation at break.

[0067] Table 2

[0068] Combined with the data in Table 2, compared with the comparative examples, the present invention uses n-hexylphosphoric acid to modify magnesium hydroxide, which improves the flame retardant efficiency. The addition of modified steel slag and modified magnesium hydroxide significantly improves its high temperature resistance and smoke suppression effect, and it can also maintain good tensile strength and flame retardant properties at 150 °C.

[0069] The above are the preferred embodiments of the present invention. Without departing from the principle of the present invention, those of ordinary skill in the art can also make several improvements and refinements, which should also be regarded as the protection scope of the present invention.

Claims

1. A preparation process of a halogen-free rubber conveyor belt, characterized in that, It includes the following steps: S1. Mix and stir n-hexylphosphoric acid and ethanol, and gradually add the mixture dropwise to a magnesium hydroxide suspension. Stir, cool, wash, and dry under vacuum to obtain modified magnesium hydroxide. S2. Grind steel slag powder, add anhydrous ethanol and mix and stir, add sorbic acid solution, stir and react, centrifuge to obtain precipitate, wash, and dry to obtain modified steel slag. S3. Immerse the pretreated aramid fiber cloth in KH-560 solution to obtain the surface-treated aramid fiber cloth. S4. Add rubber, modified steel slag, carbon black, modified magnesium hydroxide, stearic acid, zinc oxide, crosslinking agent, and sulfur into a two-roll mill for mixing. After thin-sheeting, calender and sheet out, and then press and mold with the surface-treated aramid fiber cloth, and cure to obtain a halogen-free rubber conveyor belt.

2. The preparation process of a halogen-free rubber conveyor belt according to claim 1, characterized in that, The magnesium hydroxide suspension is prepared by mixing magnesium hydroxide particles and anhydrous ethanol and performing ultrasonic treatment for 5 - 10 min.

3. The preparation process of a halogen-free rubber conveyor belt according to claim 1, characterized in that, In step S1, mix and stir n-hexylphosphoric acid and ethanol for 10 - 15 min, gradually add the mixture dropwise to the magnesium hydroxide suspension, evacuate, stir at a speed of 2000 r / min for 10 - 20 min, then raise the temperature to 170 °C, stir at a speed of 300 r / min for 6 h, cool to room temperature, rinse with anhydrous ethanol 2 - 3 times, and dry under vacuum at room temperature for 8 - 12 h to obtain modified magnesium hydroxide.

4. The preparation process of a halogen-free rubber conveyor belt according to claim 1, characterized in that, In step S2, the mixing and stirring speed is 500 r / min and the time is 10 min, the stirring reaction temperature is 80 - 150 °C and the time is 2 - 3 h, wash with anhydrous ethanol 2 - 3 times, and the drying temperature is 100 - 120 °C and the time is 6 h.

5. The preparation process of a halogen-free rubber conveyor belt according to claim 1, characterized in that, In step S2, the mass concentration of the sorbic acid solution is 14%.

6. The preparation process of a halogen-free rubber conveyor belt according to claim 1, characterized in that, The pretreated aramid fiber cloth is obtained by ultrasonically cleaning the aramid fiber cloth with acetone for 1 h, washing with deionized water 3 - 5 times, immersing it in a 5% CaCl₂ ethanol solution for 5 h, then immersing it in a 10% NaOH aqueous solution, immersing at 65 °C for 3 - 5 h, rinsing with deionized water 2 - 3 times, and air-drying.

7. The preparation process of a halogen-free rubber conveyor belt according to claim 1, characterized in that, In step S3, immerse the pretreated aramid fiber cloth in a 10% KH-560 solution and immerse at 40 °C for 3 - 5 h to obtain the surface-treated aramid fiber cloth.

8. The preparation process of a halogen-free rubber conveyor belt according to claim 1, characterized in that, In step S4, the rubber is natural rubber, silicone rubber, and carboxy styrene butadiene rubber, the crosslinking agent is di-tert-butyl peroxide, and antioxidant 1010 is added when adding the crosslinking agent.

9. The preparation process of a halogen-free rubber conveyor belt according to claim 1, characterized in that, In step S4, the mixing is carried out at 45 - 70 °C, the number of thin-sheeting times is 5 - 7 times, the curing temperature is 160 °C, and the time is 30 - 50 min.

10. A halogen-free rubber conveyor belt prepared by using the preparation process of a halogen-free rubber conveyor belt according to any one of claims 1 to 9, characterized in that, It includes raw materials in the following mass parts: 100 parts of rubber, 20 - 30 parts of modified steel slag, 10 - 20 parts of carbon black, 10 - 15 parts of modified magnesium hydroxide, 8 - 10 parts of stearic acid, 2 - 3 parts of zinc oxide, 0.3 - 0.5 parts of crosslinking agent, 5 - 7 parts of sulfur, and 1 - 2 parts of antioxidant 1010.

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